Cationic lipid-mediated gene transfer (lipofection) is a simple and efficient technique for introducing foreign genetic information into cultured mammalian cells (P. L. Feigner et al., Proc Natl Acad Sci USA (1987) 84:7413-17; P. L. Feigner et al., Ann NY Acad Sci (1995) 772:126-39). Although it is a widely used gene transfer technique, it is hampered by several disadvantages, including low gene transfer efficiency in some cell types, instability and serum-induced inactivation of the DNA-lipid complex, and cell toxicity of the lipofection procedure. In most cell lines, cationic liposome-mediated transfection requires serum depletion.
A number of approaches have been tried to overcome these disadvantages. H. E. Hofland et al., Proc Natl Acad Sci USA (1996) 93:7305-09, reported the formation of stable DNA-lipid complexes that retain their efficiency of gene transfer even in the presence of serum in culture medium, and that remain active for up to three months. Mizuguchi et al. reported that the fusogenic liposomes formed by cationic lipid-DNA complex and Sendai virus retained 70% of their transfection efficiency even in the presence of 40% fetal bovine serum (FBS) in contrast to the virtual inactivity of complexes formed without Sendai virus, even in the presence of as little as 5% FBS.
The polycation polybrene is used routinely to enhance the efficiency of retrovirus vector-mediated gene transfer. S. Andreadis et al., Hum Gene Ther (1997) 8:285-91, have recently reported that the concentrations of polybrene required for optimum retrovirus-mediated gene transfer increase with increasing concentrations of serum. X. Gao et al., Biochemistry (1996) 35:1027-36, have also reported that the efficiency of cationic liposome mediated gene transfer in vitro can be enhanced up to 2 to 28-fold by the use of a polycation. Adding a polycation during DNA-lipid complex formation resulted in complexes having a reduced particle size, leading to higher efficiency.